MRAM (Magnetic Random Access Memory) is a memory device using a storage element having a magnetoresistive effect for a memory cell that stores information. MRAM attracts attention as a next-generation memory device featuring the high-speed operation, large capacity, and non-volatility.
The magnetoresistive effect is a phenomenon in which electric resistance changes in accordance with the magnetization direction of a ferromagnetic substance. In MRAM, the magnetization direction of such a ferromagnetic substance is used to record information and information is read based on the magnitude of electric resistance corresponding thereto. Accordingly, MRAM can be caused to operate as a memory device.
In recent years, a ferromagnetic tunnel junction including two CoFeB ferromagnetic layers and an MgO tunnel barrier layer formed therebetween is used in a magnetoresistive effect element. In the ferromagnetic tunnel junction, a huge MR (Magnetic Resistance) ratio of 100% or more can be obtained due to the TMR (Tunnel Magnetic Resistance) effect. Thus, large-capacity MRAM using an MTJ (Magnetic Tunnel Junction) element making use of the TMR effect attracts expectations and attention as a magnetoresistive effect element.
When an MTJ element is used to MRAM, one of two ferromagnetic layers sandwiching the tunnel barrier layer therebetween is set as a reference layer in which the magnetization direction is invariable and the other is set as a storage layer in which the magnetization direction is variable. Information can be stored by associating a state in which the magnetization direction of the reference layer and the magnetization direction of the storage layer are parallel and a state in which both magnetization directions are antiparallel with “0” and “1”. When compared with a case in which both magnetization directions are antiparallel, the resistance (barrier resistance) of the tunnel barrier layer is smaller and the tunnel current is larger when both magnetization directions are parallel.